2017趋势科技校园招聘算法题

题目：现有给定升序排列的整形数组a
和整数S，需要在整型数组中找到任意个小标，使得各小标对应数字之和为S，输出所有可能的下标组合。

例如：

数组 1,4,8,10,12,15,22,25,31， X=30 可得

下标： 2,6  ： a[2] + a[6] = 30

下标：0,1,3,5 ： a[0] + a[1] + a[3] + a[5] = 30

...

使用下面的函数原型

int searchNumbers(int data[], unsigned int length, int sum)

[思路] 回溯法，每个位置有两种情况可取可不取，可得出所有的情况。

代码如下：

#include<iostream>
#include<vector>
using namespace std;

void DFS(int data[], unsigned int length, int target, int &sum, int depth, vector<int> &v, vector<vector<int> >&vv)
{
if (depth == length)
return;
if (sum == target)
{
vv.push_back(v);
}
if (sum < target)
{
DFS(data, length, target, sum, depth + 1, v, vv);

sum = sum + data[depth];
v.push_back(depth);
DFS(data, length, target, sum, depth + 1, v, vv);
sum = sum - data[depth];
v.pop_back();
}
}
int searchNumbers(int data[], unsigned int length, int target)
{
int sum = 0;
int depth = 0;
vector<int> v;
vector<vector<int> >vv;

DFS(data, length, target, sum, depth, v, vv);

for (int i = 0; i < vv.size(); i++)
{
v = vv[i];
for (int j = 0; j < v.size(); j++)
cout << v[j] << " ";
cout << endl;
}
return vv.size();
}

int main()
{
int data[] = {1,4,8,10,12,15,22,25,31};
unsigned int length = sizeof(data) / sizeof(data[0]);
int target = 30;

int answer = searchNumbers(data, length, target);
cout << "total number: " << answer << endl;
return 0;
}